1. Field of the Invention
This invention relates to a novel aliphatic triisocyanate, a method of its preparation and a hardener for a non-yellowing polyurethane resin comprising the aliphatic triisocyanate.
2. Description of the Prior Art
It is known that aliphatic polyisocyanates can be employed as starting materials for producing non-yellowing polyurethane resins having good weatherability. Exemplary aliphatic polyisocyanates of non-yellowing type include hexamethylene diisocyanate, 2,2,4- and 2,4,4-trimethylhexamethylene diisocyanate. These diisocyanates, however, have irritant odor at ordinary temperature and toxicity to human bodies and thus disadvantageously it is difficult to safely handle these diisocyanates. Accordingly, they are employed in the form of their adducts by reacting the diisocyanates with a diol such as ethylene glycol and butanediol or a triol such as trimethylolpropane as a so-called agent for producing the adduct. But the adducts become polymer mixtures having a high viscosity and should be diluted with a solvent from the standpoint of their easy handling.